The climate was definitely very different back then. So that would have affected the flora, and there was also a whole bunch of megafauna alive back then that have since gone extinct, likely taking a lot of their gut microbiome with them, since we know that the bacteria and parasites living inside larger animals can be species-specific. I think to the roundworms' perception, there'd actually be a lot of changes in the soil that they would pick up on, that we wouldn't. Like, you know, maybe they were used to eating mammoth poop and now they're in a lab after being woken up, they're eating something that just tastes weird to them because it's not what they were used to. Even pretty simple animals can recognise and respond to changes in their environment, even if they don't question it cognitively.